Our invention relates to an improved multifrequency generator, and particularly to such a generator for supplying one of a plurality of selectable frequencies with minimum noise sideband components to a radio transmitter and a radio receiver.
In two-way radio communication, it is desirable for a radio transmitter and radio receiver (sometimes called a transceiver) to transmit and receive on a plurality of different radio frequency channels. This is particularly true where, in a given geographical area, there are a plurality of such channels available to a user. In such an area, a user can avail himself of one of these channels by switching his radio equipment until an idle channel is found, or by having equipment that automatically switches his radio equipment to an idle channel.
Accordingly, a primary object of our invention is to provide a new and improved multifrequency generator for a radio transmitter and/or a radio receiver.
Another object of our invention is to provide a new and improved multifrequency generator that can be readily shifted to a desired frequency in a group or band of frequencies.
In two-way radio communication, duplex operation is often desired so that a user can transmit and receive at the same time, as in a normal conversation. This duplex operation usually requires two different frequencies, one for transmitting and one for receiving.
Accordingly, another object of our invention is to provide a new and improved multifrequency generator that can selectively produce two different frequencies with minimum noise component content in a group or band of frequencies.
Another object of our invention is to provide a new and improved multifrequency generator that has a single control that enables the generator to produce a selected transmitting frequency and a selected receiving frequency from a group or band of frequencies.
In today's radio systems, frequency stability must meet all legal requirements. Such stability can usually only be achieved by the use of piezoelectric crystal oscillators. If the number of selectable frequencies is relatively high, a separate crystal for each frequency for the radio transmitter and a separate crystal for each frequency for the radio receiver is economically undesirable or impractical.
Accordingly, another object of our invention is to provide a new and improved multifrequency generator that requires relatively few crystal oscillators.
Another object of our invention is to provide a new and improved multifrequency generator that requires one relatively low frequency oscillator for all channel frequency signals, a second crystal oscillator which may be modulated for all transmitter frequency signals, and a third crystal oscillator for all receiver frequency signals if different from the transmitter frequencies.